Method for treating cellulose and product thereof



Patented Feb. 24, 1953 METHOD FOR TREATING CELLULOSE AND PRODUCT THEREOFWalter P. Ericks, Lockport, N. Y., assignor to The Upson Company,Lockport, N. Y., a corporation of New York No Drawing. Application July7, 1949, Serial No. 103,527

8 Claims.

This invention relates to dimensionally stabilized materials ofcellulose fibers, particularly cellulose structural materials, andtomethods for stabilizing such materials against dimensional change causedby change in the humidity of the environment surrounding such cellulosematerials. More particularly, the invention relates to the stabilizationof structural cellulose fiber boards as well as wood and paper andfabrics made of cotton, linen and other cellulose materials to renderthem more resistant to dimensional changes resulting from variations inthe ambient humidity and to improve the strength of such products.

It is well known that materials made up entirely or predominantly ofcellulose fibers expand and contract with variations in humidity in theambient atmosphere, such materials suffering an increase in theirdimension upon absorption of moisture from the atmosphere and acontraction when moisture is given up to the atmosphere upon a decreasein the humidity thereof. It is also well known that in articles whereinfibers are directionally oriented, such expansion and contractionusually occurs to the greatest extent in a direction perpendicular tothe predominant direction of the fibers. The present invention is,therefore, adapted particularly in preventing or minimizing thedimensional change which occurs across the fibers with change inhumidity in cellulose materials, although it also reduces dimensionalchange in the direction of the fibers with humidity change.

Various expedients have been heretofore employed for the purpose ofdimensionally stabilizing materials made up predominantly of cellulosefibers as, for instance, plywood, wood boards, pulp products andcombinations thereof, and solid paper boards. A degree of dimensionalstabilization is obtained in the manufacture of plied or laminatedarticles by arranging the laminations with their fiber directionsdisposed angularly to one another rather than parallel. Althoughimprovement in [dimensional stabilization is obtained, the operation islaborious since it requires cutting and proper selection and assemblageof the plies.

It has also been suggested to densify the prod- 2 filed November 10,1945, and now abandoned, of which this is a continuation-in-part, aswell as my copendin application Serial No. 95,872, filed May 27, 1949, Ihave disclosed that certain oructs under heavy pressure and to therebyset the cellulose fibers. Very expensive presses and extensive auxiliaryequipment is required for this structural cellulose fiber board.

In my copending application Serial No. 627,966,

ganic compounds having at least two hydroxyl groups in their molecules,particularly partial esters of polycarboxylic acids and polyhydricalcohols having at least one hydroxyl group in the residue derived fromthe polyhydric alcohol and at least one carboxyl group in the residuederived from the carboxylic acid, stabilizes structures made uppredominantly of cellulose fibers against expansion and contraction dueto variation in atmospheric humidity. I have disclosed in my copendingapplication Serial No. 103,526, filed July '7, 1949, that othercompounds having both hydroxyl and carboxyl groups, such as hydroxycarboxylic acids, also are eifective stabilizers against such expansionand contraction. In my copending application Serial No. 103,528, filedJuly '7, 1949, I have also disclosed that polycarboxylic acids have asimilar stabilizing efiect.

In accordance with the present invention, I have found that materialsmade. up predominantly of cellulose fibers may be wholly or partiallystabilized against dimensional change by introducing into such cellulosematerials certain specified chemical compounds which also appear to havea particular afiinity for the cellulose fibers. Compounds which producedimensional stabilization are organic in nature and have at least twohydroxyl groups and possess certain other characteristics with respectto volatility. The series of compounds possessing dimensionalstabilizing characteristics are the polyhydric alcohols.

The polyhydric alcohols are usually either soluble in water or in lowmolecular weight aliphatic alcohols or ketones or mixtures of thesesolvents. When in solvent solution, they rapidly penetrate into thefibrous structures, between the fibers and into the fiber cells, and infact many of them rapidly penetrate such fibrous structures even in theabsence of a solvent. In most cases, however, reater dimensionalstability is obtained when the polyhydric alcohols are employed insolution in a solvent for impregnating the fibrous structures. Furtherproperties and characteristics of the stabilizing chemicals will be morefully described hereinafter.

For purposes of illustration only, the invention will be described indetail in its application to the production of dimensional stability inlaminated structural cellulose fiber boards. Such products are bestexemplified upon the market by the structural building panels sold underthe name Upson Board. These cellulose fiber boards are generallymanufactured from socalled fiber boards, that is, a fiber sheet with acaliper'greater than about 0.030 inch. These fiber boards are assembledand bonded to one another to produce a laminated or plied articlehaving, for instance, from two to about seven plies. The resultinglaminated structural cellulose fiber board occurs in standard sizedpanels of from A; inch to inch or more in thickness, and of specifiedlengths and widths. The original cellulose board is manufactured fromany conventional type of cellulose pulp stock as, for instance, groundwood fiber, chemical Wood fiber, rag fiber and other conventional pulpfibers and mixtures thereof. The initial cellulose board whichconstitutes the individual ply may be made either upon a conventionalcylinder machine, as is generally the case, or may be made upon aFourdrinier machine. It will be understood, however, that the inventionis of general application to structural cellulose materials as, forinstance, fiber insulation board, sound absorbing board, table topboard, structural board for the interior of an airplane, and the like.

The compounds employed to effect stabilization in the structuralcellulose fiber board against dimensional change induced by change inhumidity may be introduced into the fibers from which the board is made,into the individual plies of the ultimate laminated structure or intothe final laminated assembly itself. The choice or the place ofintroduction of the stabilizing compounds and the manner in which it isto be introduced will be dictated by the type of fiber available and thetype of structural panel to be produced.

Thus, when operating a closed board machine system wherein all water isrecycled, the impregnating compound may be added to the beater or to thestock prior to paper formation, as for instance in the head chest,assuming that a sta- V bilizing compound has been chosen which is notreadily subject to hydrolytic change at the tem- 1 perature and pH ofthe pulp suspension. Or, the impregnating compound may be added at anyother point in the wet end of the machine.

Where the individual cellulose structural board is already formed, thestabilizing compounds may be introduced into the board by immersing theboard in a compound or a solution thereof or by impregnating the boardwith a spray containing the treating compound or by applying it withpadding rolls, all conventional methods of impregnation. Where alaminated board has alreadybeen formed by bonding a plurality ofindividualboards together, the resultant laminated article may beimmersed in the stabilizing com pounds or a solution thereof and theimpregnated board subsequently dried. The impregnation under suchcircumstances will generally be desirably performed by subjecting theboard to vacuum, at which time occluded gases and volatile materials areremoved from the board, then permitting the impregnating solution toflow into the evacuated chamber containing. the board generally placedtherein in an upright position and spaced apart, whereby the boards areenveloped .in the solution which is, in effect, forced into the boards.This penetration of the solution may then be increased by relieving thevacuum and, if desired, raising the pressure above that of theatmosphere to enhance the speed and depth of penetration.

iii)

It is therefore an object of the present invention to provide a simpleand inexpensive impregnating method for dimensionally stabilizing andstrengthening structures made up substantially of cellulose and toproduce dimensionally stabilized cellulose products.

In broad aspect, therefore, the invention comprehends the incorporationinto structural cellulose fibrous materials of a polyhydric alcohol ormixture of such alcohols whereby the usual expansion and contraction ofsuch cellulose materials is considerably minimized by reason of changein humidity conditions in the atmosphere surrounding such materials.This stabilizing effect is dependent upon the quantity of thestabilizing compound incorporated in the fibrous cellulose structuralelement. Effective dimensional stabilization has been accomplished byincorporating in the fibrous material from about 2 to.50% of thestabilizing compound based upon the weight of oven driedfiber. The exactquantity to be incorporatedv into the cellulose material will bedictated by the type of material, the type of polyhydric alcoholemployed as a stabilizing compound, and the amount of the usualexpansion or contraction which it is desired to remove. Thus, undercertain conditions of use, the removal of so little as 12 or 15% of thenormal expansion or contraction of a cellulose structural materialmay besuitable, while in other conditions of use, it may be desired to remove50, 60 or 10% or more of the normal expansion or contraction encounteredwith a particular change in humidity conditions in the surroundingatmosphere. v

The stabilizing compound may be incorporated into the cellulose'fibers,whether the same be in fibrous form, unfibrated or felted fibrous form,by the employment of aqueous solutions, solutions in hydrophilicsolvents, or mixtures thereof with water or in some instances may beincorporated without the employment of a solvent. However, the usualmode of incorporation will be to employ as an impregnating solution anaqueous or hydrophilic solution of the stabilizing compound.

The cellulose structural materials may be treated with the impregnatedstabilizing material or solution thereof at substantially any desiredtemperature, although the usual impregnating temperatures will rangebetween 20 C. and 50 C. However, temperatures as high as C. mayfrequently be employed.

While the actual mechanism of the stabilizing action of the presentinvention for cellulose fibers isnot fully understood. it is believedthat their penetrating power and their fixation on and in the cellulosefibers is due to the particular molecular structure, that is to say, thepresence of hydroxyl groups in both the cellulose and the stabilizingmaterial.

After their incorporation in the cellulose material to be dimensionallystabilized, the stabilizing compounds show considerable resistance toremoval by water and solvents, and it is believed, therefore, thatprobably there is some loose form of physico-chemical combinationbetween the cellulose molecule and the stabilizing chemical. Thisresistance to removal of the stabilizers by Water and solvents is quitemarked, particularly if the impregnated cellulose products are heated toelevated temperatures as, for instance, between 100 C. and 200 C. It isfurther believed that the fixation of the stabilizing materials in andon the cellulose fiber may be due to the ability of the molecules of thestabilizing materials to react with each other, as well as with thecellulose, whereby polymerization takes place with the formation of longchain molecules of high molecular weight. The. presence of hydroxylgroups in the polyhydric alcohol suggests that, on heating, the hydroxylgroups of th polyhydric alcohol react with the hydroxyl groups of thecellulose to modify the chemical structure of the latter. It is believedthat such modification of the cellulose results in increased dimensionalstability of the cellulose structural material and also increases itsstrength and water resistance.

The fixation of the stabilizing compounds in and on the cellulose fiberscan be enhanced by employing them in combination with thermosettingresins, which in. their partially reacted state are soluble in thevolatile, hydrophilic solvents for the stabilizers such as water, lowmolecular Weight alcohols and ketones or mixtures thereof. Thethermosetting resins, after setting, are believed to cover and protectthe stabilizing materials in and on the cellulose fibers from attack bysolvents. In this connection, it is further believed that thestabilizing materials penetrate farther into the cellulose fibers thanthe thermosetting resins, thus producing a protective coating ofthermosetting resins.

The incorporation of thermosetting resins into the cellulose structuremodifies to some extent the effect of the polyhydric alcohol in such away that the hardness and. water resistance of the resulting cellulosefiber structures impregnated by the stabilizers are increased. Therequirement of the properties determined by the ultimate use of theresulting article will guide the selection of the stabilizing materialand its use either separately or jointly with a thermosetting resin.

Suitable thermosetting resins which may be employed in combination withthe stabilizing material of the present invention include phenolformaldehyde, urea formaldehyde, and melamine formaldehyde, which aresoluble in the volatile, hydrophilic solvents employed. Any otherthermosetting resins which in their partially reacted state have theproperty of being soluble in such solvents may also be employed. Theresins become insoluble and infusible upon advancement and preventattack by water or solvents upon the stabilizing materials and reactionproducts thereof deposited in and on the cellulose fibers. The amount ofthermosetting resin may be varied within a considerable range, forexample, between and 50% of thermosetting resin in the final cellulosefiber product based on the dry weight of fiber.

The advantages gained in impregnating articles made up of cellulosefibers with polyhydric alcohols alone and in combination withthermosetting resins are shown by the following examples which are to betaken in an illustrative rather than a limiting sense. In securing thedata for such examples the procedure outlined below was followed.

A board prepared on a cylinder paper machine from used news fiber wascut into strips measuring 0.051 x 2" x 12", extending in its largestdimension perpendicular to the predominating direction of fibers in theboard. The strips were immersed into the impregnating solution kept at50 C. and they were allowed to remain therein until the board was wetterto its center.

The time required for complete impregnation was within a range of 1 to 8minutes, and on the average was about 4 minutes.

The dry strip was weighed before impregnation and, after the immersionin the impregnant, dried by heating at 125 C. for 30 minutes. From thedifference in weight, the quantity of dimensional stabilizingingredients deposited within the board, in and on the fibers, wasdetermined. The strips were accurately measured dry and then conditionedin a humidifying chamber, kept at 'relative humidity and 38 C. for about48 hours,

at the end of which period the strips had absorbed' a maximum ofmoisture and usually showed no further increase in expansion. The totalexpansion of each of the unimpregnated control strip and of theimpregnated and dimensionally stabilized strip was thus determined. Thedifference in the amount of expansion between the control strip and thestabilized strip represents the amount of normal expansion removed bymeans of the dimensional stabilization treatment; the difference inexpansion between the two strips divided by the total expansion of thecontrol strip times is the percent of normal expansion removed.

The flexural strength of the strip was determined by the known method ofapplying a load required to break the strip.

Example 1 Cellulose fiber boards were impregnated with solutionscontaining equal parts by weight of ethylene glycol and a thermosettingcresol-formaldehyde resin. The total quantity of ethylene glycol andcresol-formaldehyde resin in solution was varied from 50% to 3.2%. Thesolvent employed was water containing some isopropanol for preventingturbidity formation in the impregnating solutions during the adjustmentof their pH to 3.5 by addition of the required quantity of 50%phosphoric acid. Impregnated boards containing 39.7%, 19.2%, 11.8% and5.9% of active ingredients, after drying and heating, lost 78%, 58%, 51%and 40% of their original contraction and expansion, respectively.

Cellulose fiber boards impregnated with aqueous solutions containingethylene glycol and a thermosetting urea-formaldehyde resin in equalquantities of varying concentrations containing 48%, 26.8%, 14.3%, 10.9%and 5.2% of impregnating ingredients, after drying and heating, showed aloss of 55%, 41%, 28%, 27% and 14% in their property of contracting andexpanding in varying humidity of the atmosphere. All impregnatedsamples, subsequent to their treatment showed also improvement infiexura1 strength and resistance to water absorption. Boards containingethylene glycol alone possessed improved plasticity and those containingboth the ethylene glycol and a thermosetting resin possessed improvedrigidity.

Example 2 Cellulose fiber boards were impregnated with diethylene glycoland its 50%, 25%, 12.5% and 3.125% aqueous solutions. The correspondingcontents of diethylene glycol in boards after their drying and heatingwere 51.8%, 41.6%, 28.8%,

'7 22 .4%, 12.4% and 10.2%, respectively, and. the losses in contractionand expansion were 74.7 77.9%, 51.5%, 37.8%, 35.6% and 20%,respectively.

Cellulose fiber boards impregnated with solutions composed of equalquantities of diethylene glycol and thermosetting cresol-formaldehyderesin dissolved in various quantities of water containing. a sufiicientquantity of isopropanol for prevention of turbidity formation, afterdrying and heating, contained 43.3%, 24%, 13.5%, 9.2% and 3.9% of activeingredients and showed losses of 84.2%, 57%, 50.5%, 38.9% and 22%,respectively, in their property of contracting and expanding in varyinghumidity of the atmospliere.

The contents of total impregnating ingredients in cellulose fiber boardsimpregnated with aqueous solutions conntaining diethylene glycol andthermosetting urea-formaldehyde resin in equal concentrations were38.3%, 21.5%, 10.4%, 5.9% and 5%. They lost 64.4%, 31%, 23.4%, 22.2% andof their contraction and expansion, respectively. All impregnated boardsshowed im-- provements in water-resistance and flexural strength.

Boards containing diethylene glycol showed improvement in plasticity andthose containing a thermosetting resin showed improved rigidity.

Example 3 Cellulose fiber boards were impregnated with triethyleneglycol and its solutions of various concentrations. After drying andheating, the

boards showed improvement in dimensional stability, varying from 19% to75%.

Cellulose fiber boards treated in like manner with solutions containingthermosetting cresolformaldehyde resin and triethylene glycol lost, inpart, their property of contracting and expanding, ranging from 19.5% to74.4%.

An improvement in dimensional stabilization ranging from 14% to 55.4%was obtained on cellulose fiber boards impregnated with solutions ofvarious concentrations containing equal quantitles of triethylene glycoland thermosetting urea-formaldehyde resin.

Example 4 Cellulose fiber boards were impregnated with propylene glycoland its solutions of various concentrations. Ihe evaluation of boardsafter drying and heating indicated that the boards lost from 31 to 94%of their original contraction and expansion. Cellulose fiber boardsimpregnated with solutions containing propylene glycol and thermosettingcresol-formaldehyde resin in the first series of impregnation andpropylene glycol and thermosetting urea-formaldehyde in the secondseries of impregnation showed, after drying and heating, a substantialimprovement in dimensional stabilization, water-resistance, rigidity andflexural strength. A further improvement of properties was obtained whenthe boards were pressed during their heat treatment.

Example 5 Cellulose fiber boards impregnated with dipropylene glycol andwith its aqueous solutions of various concentrations contained, afterdrying and heating, from 8.2% to 46.4% of dipropylene. Their evaluationindicated that their dimensional stability was improved by 34% to 90%,respectively. Impregnated fiber boards containing,

after drying and heating, 5.2% to 39.8% 01 dipropylene glycol andthermosetting cresol-formaldehyde resin in equal quantities, showedimprovement in dimensional stability ranging between 26.6% to 71%,respectively, and those containing 3.9% to 43.2% of dipropylene glycoland thermosetting urea-formaldehyde resin showed improved dimensionalproperties ranging from 12% to 59.1%, respectively.

All impregnated and subsequently heat treated boards showed improvedflexural strength and resistance to water.

Example 6 Cellulose fiber boards impregnated with aqueous solutions ofvarious concentrations of polyethylene glycol having an averagemolecular weight of 200, and known to the trade as "Polyethylene Glycol200, contained after drying and heating, 10.5% to 48.2% of PolyethyleneGlycol- 200. Their evaluation showed that their dimensional stabilitywas improved by 18.9% to 81.1%, respectively. Impregnated cellulosefiber boards containing, after drying and heating, 6.1% to 40% ofPolyethylene Glycol 200, and thermosetting cresol-formaldehyde resin inequal proportions, lost 21.4% to 84.2% of their original contraction andexpansion in varying humidity of the atmosphere.

Impregnated and heat treated boards containing polyethylene glycol andthermosetting ureaformaldehyde resin in equal proportions also showed asubstantial improvement in dimensional stabilization.

Fiber boards were impregnated with isopropanol solutions containing 2%,4%, 8% and 16% of stabilizing impregnant composed of equal quantities ofPolyethylene Glycol 200 and a polymerized rosin known to the trade asPolyPale Resin. The impregnated and heat treated boards containing 5%,8.3%, 13.1% and 23.6% of the stabilizing impregnant lost 25.6%, 28.9%,33.3% and 40%, respectively, of their properties of contracting andexpanding in varying humidity of the atmosphere.

Fiber boards were impregnated with acetone solutions containing 4%, 8%,16% and 32% of a solute composed of equal quantities of PolyethyleneGlycol 200 and a hydrogenated rosin ester known to the trade asStaybelite Ester #10. The impregnated and heat treated boards contained6%, 6.3%, 14.3% and 23% of the above solute and showed 14.2%, 16.4%,21.6% and 33% loss in their contraction and expansion properties.

All impregnated and heat treated boards showed improvements inwater-resistance and flexural strength.

Example 7 Cellulose fiber boards were impregnated with polyethyleneglycols having average molecular weights of 300, 400 and 600 and knownto the trade as Polyethylene Glycol 300, 400 and 600, respectively, andwith their aqueous solutions of various concentrations. The impregnatedand heat treated boards showed substantial improvemerits in dimensionalstability when they were allowed to remain in varying humidity of theatmosphere.

Cellulose fiber boards were also impregnated with solutions of variousconcentrations containing in equal quantities one of the abovepolyethylene glycols and one of the following resins:cresol-formaldehyde, urea-formaldehyde, Poly- Pale Resin and StaybeliteEster #10. All impregnated and heat treated boards showed im- Qprovements in dimensional stability, water-resistance and flexuralstrength.

Example 8 Cellulose fiber boards were impregnated with aqueous solutionsof various concentrations containing polyethylene glycols having averagemolecular weights of 1000, 1500, 1540, 4000 and 6000 and known to thetrade as Carbowax 1000, 1500, 1540, 4000 and 6000, respectively. Boardswere also impregnated with solutions of various concentrationscontaining in equal quantities one of the above Carbowaxes and athermosetting resin.

All of the impregnated and subsequently heat treated boards showedimproved dimensional stability in varying humidity of the atmosphere,water-resistance and fiexural strength.

Example 9 A cellulose fiber board strip was impregnated with1,5-pentanediol which was subsequently heated for 30 minutes at 125 C.It was found that the board contained 48.2% of 1,5-pentanediol and thatits dimensional stability in varying humidity of the atmosphere wasimproved by 80%.

It was found that when cellulose fiber boards were impregnated withaqueous solutions containing 3.12%, 6.25%, 12.5%, 25% and 50% of1,5-pentanedio1 as stabilizing impregnant, the impregnated boardscontained, after drying and heating, 5.3%, 7.9%, 13.2%, 25.2% and 43.1%of the stabilizer, respectively, and that they lost 19.1%, 39.2%, 60.8%and 92%, respectively, of their contraction and expansion in varyinghumidity of the atmosphere.

Impregnated and heat treated boards containing 6.2%, 9.7%, 15.1%, 24.8%and 45.2% of dimensional stabilizing ingredients composed of equalquantities of 1.5-pentanediol and thermosetting urea-formaldehyde resinlost 24.6%, 42%, 45.2%, 56.9% and 73.1% of their contraction andexpansion in varying humidity of the atmosphere.

Cellulose fiber boards impregnated with solutions containing variousconcentrations of a solute composed of equal quantities of1,5-pentanediol and thermosetting cresol-formaldehyde resin contained,after drying and heating, 6.3%, 8%, 17.2%, 29.8% and 42% of the abovesolute with a corresponding loss of 26.8%, 45.1%, 53.6%, 74.4%. and 92%,respectively, of contraction and expansion in varying humidity of theatmosphere.

Example 10 Cellulose fiber boards were impregnated with glycerol and itsaqueous solutions containing 50%, 25%, 12.5%, 6.25% and 3.125% glycerolas a dimensional stabilizer. The impregnated boards contained, afterdrying and heating, 68%, 52%, 33%, 17%, 11% and 6% of glycerol,respectively, and showed a loss in contraction and expansion inquantities amounting to 90%, 78%, 53%, 23%, 11% and 9%, respectively.

Cellulose fiber boards impregnated with a solution of variousconcentrations containing equal quantities of glycerol and thermosettingcresolformaldehyde resin as stabilizer contained, after drying andheating, 44%, 25%, 13%, 6.7% and 5.1% of the above solute; theirdimensional stabilization was improved by 69%, 57%, 33%, 31% and 11%,respectively.

Example 11 various concentrations and with solutions of variousconcentrations containing equal quantities of mannitol and thermosettingmelamineformaldehyde resin showed, after drying and heating, improveddimensional stability, waterresistance and fiexural strength.

Example 12 Cellulose fiber boards impregnated. with solutions of variousconcentrations containing sorbitol and solutions of variousconcentrations containing sorbitol and cresol-formaldehyde, showed,after drying and heating, improved dimensional stability,water-resistance and fiexural strength.

Example 13 Cellulose fiber boards impregnated with 25%,.

12.5%, 6.25% and 3.125% of pentaerythritol aqueous solutions contained,after drying and heating, 39%, 18%, 12%, and 4.9% of pentaerythritol,respectively, and showed, under varying humidity of the atmosphere,reductions in contraction and expansion by 88%, 66%, 37% and 21%,respectively.

Cellulose fiber boards impregnated with solutions of variousconcentrations containing equal quantities or pentaerythritol andmelamineformaldehyde thermosettlng resin showed, alter drying andheating, improved dimensional stability, rigidity, water-resistance andiiexural strength.

Example 14 Aqueous solutions containing 3.125%, 6.25%, 12.5% and 25% ofresorcinol were prepared and employed in impregnation of finer board byimmersion of the board therein. Impregnated boards containing 4%, 11%,17% and 33% of resorcinol lost, after drying and heating, 27 50%, 63%and 89%, respectively, of their original property of contracting andexpanding in varying humidity of the atmosphere. Cellulose fiber boardsimpregnated with solutions of various concentrations containing equalquantities of resorcinol and cresol-i'ormaldehyde resin as dimensionalstabilizer dissolved in isopropanol contained 8.6%, 9.3%, 16% and 29% oftotal stabilizer and showed a loss of 27%, 36%, 42% and 45%,respectively, in their property of expanding and contracting in varyinghumidity of the atmosphere.

Cellulose fiber boards were impregnated with solutions of variousconcentrations composed of equal quantities of resorcinol andurea-formaldehyde resin dissolved in solvent composed of equalquantities of isopropanol and water. The boards, after drying andheating, contained 5%, 8.6%, 16% and 29% of total stabilizer and lost9.2%, 20%, 33% and 41% of their original ability of contracting andexpanding in varying humidity of the atmosphere.

All impregnated and heat treated boards showed improvedWater-resistance, rigidity, flexural strength and resistance to attackby insects and micro-organisms.

Example 15 Cellulose fiber boards, impregnated with solutions obtainedby dissolving in water various quantities of hydroquinone, contained 7%,9.7%, 11% and 22% of the hydroquinone stabilizer and lost 35%, 40%, 57%and 99%, respectively, in their original property of contracting andexpanding in varying humidity of the atmosphere. Hydroquinoneimpregnating solutions containing either cresolor urea-formaldehyderesin were also effective in producing a substantial stabilization incellulose fiber boards.

Example 16 Cellulose fiber boards impregnated with solutions containingcatechol alone or in combination with hydrophilic thermosetting resinsacquired, after heating, improved dimensional stability,water-resistance and resistance to decay.

Where impregnation of the fibers is attempted prior to the preparationof a fiber board, economic and operational restrictions will narrow theselection of the polyhydric alcohols employed under such circumstancesto those which are soluble in water. Comminuted cellulose fibers can beimpregnated, however, with the stabilizing chemicals dissolved inorganic solvents and structural members made therefrom show excellentdimensional stability under extremes of humidity conditions. This isshown in the following example:

Example A An aqueous pulp suspension of a consistency of 1% was preparedcontaining 3% concentration of catechol based on solution. Sheets offiber board were prepared from this pulp, cut to size and the expansiondetermined by increasing the humidity from to 90%. When this expansionwas compared with that of board made from another portion of the samepulp without the presence of the stabilizer, it was found that a 9.7%content of the polyhydric alcohol in the board, based on the weight ofdry fiber, eliminated 42% of the normal expansion.

The same type of results were obtained when applying a solution of thestabilizing chemicals to the wet end of the pap-er making machine. Thisoperation gives somewhat greater flexibility in the choice ofstabilizing compound to be employed, as compared with addition to thebeater or head chest, for example, since it is entirely practicable touse organic solvent solutions of the stabilizer, for instance, asolution made of 25% water and 75% isopropyl alcohol and containing 2%concentration of carbowax 1500 and 5% cresol-formaldehyde thermosettingresin. When applying such a solution to the Wet lap in amounts toprovide 10.2% of impregnant in the board on a dry fiber basis,reductions in the normal expansion of 35.2% were obtained. At theselower dilutions, good results were obtained but, in many instances,operating technique will dictate the employment of relativelyconcentrated solutions when application is made to the wet lap.

Laminated cellulose structural fiber board may be impregnated with thedimensional stabilizer in any suitable fashion although immersion in thedimensional stabilizer or a solution thereof is recommended. In general,the temperature of the liquid in which the laminated cellulosestructural fiber board is immersed will be at room temperature. Where alaminated product of an exceptionally high caliper is to be impregnated,the temperature of the liquid may be elevated to facilitate penetration.The laminated board may be soaked in the impregnating solution untilsuch time as the desired quantity of dimensional stabilizer has beenabsorbed by or combined in some physico-chemical manner with thecellulose.

It may be found expedient when treating laminated cellulose structuralfiber boards, or other cellulose elements which are relatively rigid, topack the same in a chamber, preferably in an upright position, havingthe boards spaced slightly apart to facilitate free circulation. It willalso be found expedient to subject the chamber to vacuum whereby gasesand other volatile materials, which interfere With free penetration ofthe solution into the board, are removed. Liquid containing thedimensional stabilizer is then admitted to the evacuated chambercontaining the cellulose material and penetration throughout the body ofthe cellulose elements is facilitated. The impregnated boards are thenremoved from the solution and passed through any conventional form ofdrier.

The term polyhydric alcohol" is employed herein with the generallyaccepted meaning, 1. e., an alcohol having more than one hydroxyl groupin its molecules. The term is therefore not intended to include allcompounds having more than one hydroxyl group in its molecules. Thus,the carbohydrates, for example the sugars, are not considered to bepolyhydric alcohols although their molecules, in general, containseveral hydroxyl groups. The carbohydrates additionally contain aldehydegroups, keto groups or lactone, furanose or pyranose rings, 1. e.,oxygen containing rings, in their molecules. Such compounds are classedas polyhydric aldehydes (aldoses), polyhydric ketones (ke-toses) orlactones, or sugars having furanose or pyranose structure, respectively,and have physical and chemical properties differing materially from thepolyhydric alcohols employed in the present invention.

Examples of the polyhydric alcohols which may be employed in the presentinvention are simple glycols such as ethylene glycol and propyleneglycol, as Well as polyalkylene glycols such as diethylene glycol,triethylene glycol and dipropylene glycol and polyalkylene glycols up toa molecular weight of 6000. Such polyalkylene glycols are commercialproducts and are sold as mixtures of various polyalkylene glycols on thebasis of molecular weight, for example, 200, 300, 600, 1000, 1500, 4000and 6000. The polyalkylene glycols of higher molecular Weight aresemi-solids but are soluble in Water in substantially all proportions.Other polyhydric alcohols are also effective stabilizers, for example,glycerol, mannito'l, sorbitol, as well as 1,5-pentanediol,pentaerythritol, resorcinol, hydroquinone, butanediol- 1,3;2-ethylhexanediol-L3; propanediol-l,3; pentanediol-l,4; hexanediol-l,6;2,2,4-tri-methylpentanediol-l,3; decanediol-LlO; pentanetriol-l,2,3;hexanetriol-1,2,5; butanetetrol-l,2,3,4; oc-tadiene 2,6 diol 4,5;heptaneheptole-l,2,3,4,5,6,7; phloroglucinol; pyrogalol and the like.

Polyhydri-c alcohols as defined above, in general, have the requisitephysical characteristics for employment in the present invention. One ofthe important physical requirements of the polyhydric alcohol employedis that it be soluble in water or volatile, water-miscible solvents, i.e., volatile hydro-philic solvents as defined below. In general, thegreater its solubility in one of such solvents the greater thepenetration of the polyhydric alcohol into the cellulose fibers and thegreater its stabilizing effect. The latter is true irrespective ofwhether the polyhydric alcohol is employed in a solvent solution duringimpregnation.

Another important physical characteristic of the polyhydric alcohol isthat it be substantially non-volatile under all temperature conditionslikely to be encountered. That is to say, it should have a boiling pointat least as high as C. and preferably higher .at atmospheric pressure.

As to the solvents which may be employed for making up an impregnatingsolution, water is the preferred solvent and will ordinarily be employedalone if the polyhydric alcohol is soluble therein as is usually thecase. If necessary to obtain solution of the polyhydric alcohol,watermiscible organic solvents such as mono aliphatic alcoholscontaining three carbon or less, or mono aliphatic ketones containingfive carbons or less may be employed either alone or in admixture witheach other or water. By way of example, methyl, ethyl and propylalcohols are particularly suitable and dimethyl, diethyl, methyl ethyl,methyl propyl or ethyl propyl ketones are also suitable. Such solventsor solvent mixtures should have a boiling point substantially below thatof the tabilizing material, i. e., a boiling point not aboveapproximately 105 C. at atmospheric pressure. Such solvents may betermed volatile hydrophilic solvents and for purposes of thisapplication, the term volatile hydrophilic solvent is defined as water,a Watermiscible organic solvent or mixture thereof having a boilingpoint not greater than 105 C.

To summarize, the tabilizing materials in accordance with the presentinvention are either aromatic or aliphatic polyhydric alcohols ormixtures thereof. In addition to such chemical requirements they shouldbe soluble in all proportions in at least one volatile hydrophilicsolvent as defined above and should have a boiling point at least ashigh as 150 C. Since solubility in volatile hydrop-ilic solvents dependsupon several factors such as the number of hydrophilic groups, forexample, hydroxyl groups, the saturation of the compound, andarrangement of carbons as well as the number of carbons, it isimpossible to more definitely specify the nature of the effectivecompounds by chemical characteristics. A similar situation exists as tothe boiling points of the efiective compounds.

The concentration of the impregnating solution can vary from 100%polyhydric alcohol in the case of low viscosity polyhydric alcohols suchas ethylene glycol, propylene glycol, glycerol, etc., down to aconcentration as low as 1% in the case of polyhydric alcohols of highmolecular weight, for example, semi-solid polyalkylene glycols. Ingeneral, however, the best results are obtained when the polyhydricalcohol is employed in a solution having a concentration ranging betweenapproximately 5 and 60%. Also in general, the dimensional stabilityobtained does not decrease proportionately with the decrease inconcentration of the impregnating solution. When very dilute solutionsare employed, a disproportionately high degree of stabilization isretained.

Thus, the concentration of the polyhydric alcohol in the impregnatingsolution may range from approximately 1 to 100% and the amount ofpolyhydric alcohol retained in the fibrous material may range fromapproximately 1 to 50%, the preferred range being between approximately3 and 50%.

The temperature of the impregnating solution during impregnation of thestructures has an efi'ect upon the results obtained. That is to say, therate of penetration of the polyhydric alcohol or solutions thereof intothe fiber board, the quantity of deposition of the polyhydric alcohol inthe board and the resulting improvement in dimensional stability in suchimpregnated fiber structures not only depend upon the concentration ofthe solution, but also depend on the temperature of the impregnatingsolution. The higher the temperature at which impregnation is carred on,the greater the amount of polyhydric alcohol retained in the board for agiven concentration of the impregnating solution and the more effectiveis the dimensional stabilization. The usual impregnating temperatureswill range between 20 C. and 60 C., although any temperature below thatat which rapid vaporization of the impregnating solution takes place maybe employed. Such temperature will not ordinarily be above C.

The affinity of the polyhydric alcohols for cellulose fibers, theirpowers of penetration and the reason for their fixation on and in thecellulose fibers is not fully understood. From a consideration of theirmolecular structure, it may be supposed that their aflinity forcellulose fibers depends upon the presence of hydroxyl groups in boththe cellulose and in the alcohol. Their power of penetration is possiblydue to the presence of balanced hydrophilic and hydrophobic groups inthe molecules which is characteristic of surface active materials. Thesetwo properties apparently facilitate the deposition of the polyhydricalcohols in and on the cellulose fibers.

The polyhydric alcohols deposited in the fibrous products exhibitconsiderable resistance to removal by water and solvents, particularlyif the impregnated fibrous products are heated during drying orthereafter to temperatures between approximately 100 and 200 C. Thisindicates the possibility of a reaction between the cellulose and thepolyhydric alcohols, or at least from physico-chemical action, to modifythe cellulose. The modification of the cellulose is beneficiallyreflected by the increased dimensional stability and the increasedstrength and decreased water absorptivity of the resulting product.

The fixation of polyhydric acohols in and on the cellulose fibers of thestructure can be enhanced by employing them in combination withthermosetting resins which in their partially reacted state are solublein water, lower molecular weight alcohols or ketones or mixturesthereof. The thermosetting resins, after setting, are believed to coverand protect the polyhydric alcohols and their reaction products in andon the cellulose fibers from attack by solvent. In this connection it isfurther believed that the polyhydric alcohols penetrate further into thecellulose fibers than the thermosetting resins, thus producing aprotective coating of the thermosetting resin on the impregnated fibers.

The incorporation of thermosetting resins into the polyhydric alcoholsolutions modifies to some extent the properties of the resultingproduct such that the hardness and water-resistance of the resultingfibrous structures are increased. The requirements of the propertiesdetermined by the ultimate use of the resulting article will guide theselection of the polyhydric alcohol and its use, either separately orjointly with the thermosetting resin.

Suitable thermosetting resins which may be employed in combination withthe polyhydric alcohols of the present invention includephenolformaldehyde, urea formaldehyde and melamine-formaldehyde resinswhich, in their partially reacted state, are soluble in the volatilehydrophilic solvents above discussed. Any other thermosetting resinswhich in their partially reacted state have the property of beingsoluble in such solvents may also be employed. The resins becomeinsoluble and infusible after ouring and prevent attack by water orother solvents upon the polyhydric alcohol and any reaction productsthereof deposited in and on the cellulose fibers. The amount ofthermosetting resin employed may be varied within a considerable range,for example between and 50% of the mixture of polyhydric alcohol andthermosetting resin in the impregnating solution and in the finalcellulose fiber product.

What is claimed is:

1. The method of stabilizing fiber boards consisting essentially offelted cellulose pulp fibers against expansion and contraction withchanges in atmospheric humidity, which process comprises, impregnatingsaid boards substantially throughout said boards with a solution in avolatile hydrophilic solvent of a mixture of a thermosetting resin andat least one polyhydric alcohol to cause said alcohol to penetratebetween the fibers and into the fiber cells, and drying and heating theresulting impregnated boards to cure said resin, said polyhydric alcoholand thermosetting resin being soluble in said volatile hydrophilicsolvent, said polyhydric alcohol having a boiling point at least as highas 150 C., said solution having a concentration of said mixture betweenapproximately 5 and 60% and said thermosetting resin constitutingbetween approximately 5 and 50% of said mixture.

2. The method of stabilizing fiber boards consisting essentially offelted cellulose pulp fibers against expansion and contraction withchanges in atmospheric humidity, which process comprises, impregnatingsaid boards substantially throughout said boards with a solution in avolatile hydrophilic solvent of a mixture of a thermosetting resin andpropylene glycol to cause said glycol to penetrate between the fibersand into the fiber cells, and drying and heating the resultingimpregnated boards to cure said resin, said thermosetting resin beingsoluble in said volatile hydrophilic solvent, said solution having aconcentration of said mixture between approximately 5 and 60% and saidthermosetting resin constituting between approximately 5 and 50% of saidmixture.

3. The method of stabilizing fiber boards consisting essentially offelted cellulose pulp fibers against expansion and contraction withchanges in atmospheric humidity, which process comprises, impregnatingsaid boards substantially throughout said boards with a solution in avolatile hydrophilic solvent of a mixture of a thermosetting resin and1,5-pentanediol to cause said 1,5-pentanediol to penetrate between thefibers and into the fiber cells, and drying and heating the resultingimpregnated boards to cure said resin, said thermosetting resin beingsoluble in said volatile hydrophilic solvent, said solution having aconcentration of said mixture between approximately 5 and 60% and saidthermosetting resin constituting between approximately 5 and 50% of saidmixture.

4. The method of stabilizing fiber boards consisting essentially offelted cellulose pulp fibers against expansion and contraction withchanges in atmospheric humidity, which process comprises, impregnatingsaid boards substantially throughout said boards with a solution in avolatile hydrophilic solvent of a mixture of a thermosetting resin andglycerol to cause said glycol to penetrate between the fibers and intothe fiber cells, and drying and heating the resulting impregnated boardsto cure said resin, said thermosetting resin being soluble in saidvolatile hydrophilic solvent, said solution having a concentration ofsaid mixtur between approximately 5 and 60% and said thermosetting resinconstituting between approximately 5 and 50% of said mixture.

5. As a product of manufacture, a fiber board consisting essentially offelted cellulose pulp fibers and containing as an impregnant distributedsubstantially throughout said board between approximately 1% and 50%,based on the weight of said board, of a mixture of a heat curedthermosetting resin and at least one polyhydric alcohol, saidthermosetting resin in partially reacted form and said polyhydricalcohol being soluble in a volatile hydrophilic solvent and saidlpolyhydric alcohol having a boiling point at least as high as C., theamount of said thermosetting resin being between approximately 5 and 50%of said mixture.

6. As a product of manufacture, a fiber board consisting essentially offelted cellulose pulp fibers and containing as an impregnant distributedsubstantially throughout said board between approximately 1% and 50%,based on the weight of said board, of a mixture of a heat curedthermosetting resin and proplyene glycol, said thermosetting resin inpartially reacted form being soluble in a volatile hydrophilic solvent,the amount of said heat cured thermosetting resin being betweenapproximately 5 and 50% of said mixture.

'7. As a product of manufacture, a fiber board consisting essentially offelted cellulose pulp fibers and containing as an impregnant distributedsubstantially throughout said board between approximately 1% and 50%,based on the weight of said board, of a mixture of a heat curedthermosetting resin and 1,5-pentanediol, said thermosettin resin inpartially reacted form being soluble in a volatile hydrophilic solvent,the amount of said heat cured thermosetting resin being betweenapproximately 5 and 50% of said mixture.

8. As a product of manufacture, a fiber board consisting essentially offelted cellulose pulp fibers and containing as an impregnant distributedsubstantially throughout said board between approximately 1% and 50%,based on the weight of said board, of a mixture of a heat curedthermosetting resin and glycerol, said thermosetting resin in partiallyreacted form being soluble in a, volatile hydrophilic solvent, theamount of said heat cured thermosetting resin being betweenapproximately 5 and 50% of said mixture.

WALTER P. ERICKS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,857,690 Mellanoif May 10, 19322,045,350 Grlifen et al June 23, 1936 2,064,384 Richter Dec. 15, 19362,185,477 Thompson et a1 Jan. 7, 1940 2,311,341 Johnston Feb. 16, 19432417,01 1 Pollard Mar. 4, 1947

1. THE METHOD OF STABILIZING FIBER BOARDS CONSISTING ESSENTIALLY OFFELTED CELLULOSE PULP FIBERS AGAINST EXPANSION AND CONTRACTION WITHCHANGES IN ATMOSPHERIC HUMIDITY, WHICH PROCESS COMPRISES, IMPREGNATINGSAID BOARDS SUBSTANTIALLY THROUGHOUT SAID BOARDS WITH A SOLUTION IN AVOLATILE HYDROPHILIC SOLVENT OF A MIXTURE OF A THERMOSETTING RESIN ANDAT LEAST ONE POLYHYDRIC ALCOHOL TO CAUSE SAID ALCOHOL TO PENETRATEBETWEEN THE FIBERS AND INTO THE FIBER CELLS, AND DRYING AND HEATING THERESULTING IMPREGNATED BOARDS TO CURE SAID RESIN, SAID POLYHYDRIC ALCOHOLAND THERMOSETTING RESIN BEING SOLUBLE IN SAID VOLATILE HYDROPHILICSOLVENT, SAID POLYHYDRIC ALCOHOL HAVING A BOILING POINT AT LEAST AS HIGHAS 150*C., SAID SOLUTION HAVING A CONCENTRATION OF SAID MIXTURE BETWEENAPPROXIMATELY 5 AND 60% AND SAID THERMOSETTING RESIN CONSTITUTINGBETWEEN APPROXIMATELY 5 AND 50% OF SAID MIXTURE.